From Food Additive to High-Performance Heavy Metal Adsorbent: A Versatile and Well-Tuned Design

A biosourced, cross-linked hydrogel-type heavy metal adsorbent is presented. Various factors such as the highly efficient chemical interactions, the various network structures, the decreased energy consumption during cross-linking, and the negligible amount of generated waste are considered when designing the adsorbent. The widely applied, naturally occurring food additive δ-gluconolactone is studied as a building block for the adsorbent. Aminolysis reactions were applied to form linear dimer precursors between diamines and δ-gluconolactones. The abundant hydroxyl groups on the dimers from δ-gluconolactone were fully exploited by using them as the cross-linking sites for reactions with ethylenediaminetetraacetic dianhydride, a well-known metal-chelating moiety. The versatility of the adsorbent and its metal-ion binding capacity is well tuned using dimers with different structures and by controlling the feed ratios of the precursors. Buffers with different pH values were used as the conditioning media to examine the swelling properties and the mechanical properties of the hydrogels, revealing that both properties can be controlled. High heavy metal chelating performance of the adsorbent was determined by isothermal adsorption kinetics, titration, and thermal gravimetric analysis. The adsorbent exhibits an outstanding chelating ability toward the three tested heavy metals (Cu­(II), Co­(II), Ni­(II)), and the maximum adsorption capacity (q_m ∼ 121 mg·g^–1) is higher than that of the majority of the reported biosourced adsorbents.